The IANA subtag "GB" is defined as :
Type: region
Subtag: GB
Description: United Kingdom
Added: 2005-10-16
Comments: as of 2006-03-29 GB no longer includes the Channel Islands and
Isle of Man; see GG, JE, IM

The IANA subtag "GB" is defined as :
Type: region
Subtag: GB
Description: United Kingdom
Added: 2005-10-16
Comments: as of 2006-03-29 GB no longer includes the Channel Islands and
Isle of Man; see GG, JE, IM

RFC5646 is used for allocating language codes.
....snip....
So I think that is probably the reason - uk means somewhere else entirely in the context of language codes, if not in the assignment of TLDs.

RFC5646 and RFC1591 both adopted ISO 3166 (Codes for representaion of Coutries) and it's derivatives, and doing this makes sense certainly in terms of language. I believe the reason the UK TLD does not follow ISO 3166 is because .uk was already adopted and registered for DNS purposes. However, because .uk is now entrenched it does make variance from this schema look "odd" especially when language/keyboard/locale selection on computers* often talks in terms of "English (United Kingdom)" etc.

Whilst a technicality, my first thought was what setting do residents of Northern Ireland choose to adopt?

RFC5646 and RFC1591 both adopted ISO 3166 (Codes for representaion of Coutries) and it's derivatives, and doing this makes sense certainly in terms of language. I believe the reason the UK TLD does not follow ISO 3166 is because .uk was already adopted and registered for DNS purposes. However, because .uk is now entrenched it does make variance from this schema look "odd" especially when language/keyboard/locale selection on computers* often talks in terms of "English (United Kingdom)" etc.

Whilst a technicality, my first thought was what setting do residents of Northern Ireland choose to adopt?

*less of an issue for standards compliant Linux users.

I really don't mind - it isn't so much that it looks odd, but it is inconsistent with most other uses. Most drop-down location list have "United Kingdom" but, every now and again, "Great Britain" is used, just to confuse!

Maybe in a few years time I'll have to use "Scotland" as the locale ...

Actually the point is, it is entirely consistent (compliant) with the official standard even though I take your point (and largely agree) that it doesn't fit with expectations.

Yes - I wasn't arguing with you. It is a bit like computer office packages* - there is the official standard, and there is what the user sees most often. The two do not always marry up to the point that the end-user thinks the standard is what is seen most often.

* I am referring to Microsoft and the Open Office standards, of course.

Gosh no-one actually argues on here, do they? I've only seen statements made with varying degrees of fervour

Really, I was agreeing with you - the drop-down menus of locations, though coming from a different starting point, are the problem. I've thought back, and until computers became ubiquitous, I don't think the term "UK/United Kingdom" was really used. Our nationality is British, the government is British etc. So, where did this UK nonsense come from? Don't bother answering - this is sufficiently off-topic (again!) - let's keep it a rhetorical question!